China says it is "gravely concerned" by Donald Trump's Golden Dome missile defence system plans, warning it could weaponise space.
The US president on Tuesday, local time, announced that a design had been selected for the aerial shield plan.
It aims to create a network of possibly hundreds of satellites to detect, track and intercept incoming projectiles.
"It will protect our homeland," Mr Trump said, adding it should be operational by the end of his term in January 2029.
China's foreign ministry spokesperson Mao Ning told a daily briefing that "China is gravely concerned" by the plans and that it would "hurt global strategic balance and stability".
"It plans to expand the US arsenal of means for combat operations in outer space, including R&D and deployment of orbital interception systems," Ms Mao said.
"The project will heighten the risk of turning the space into a war zone and creating a space arms race, and shake the international security and arms control system.
"This is yet another 'America First' initiative that puts the US's absolute security above all else."
The Pentagon has warned for years that new missiles being developed by China and Russia are so advanced that better defence mechanisms are necessary.
In a joint statement earlier this month, China and Russia called the Golden Dome idea "deeply destabilising in nature," warning it would turn "outer space into an environment for placing weapons and an arena for armed confrontation".
What is Golden Dome?
The Golden Dome system was inspired at least in part by Israel's Iron Dome system, which has provided land-based protection from missiles and rockets since 2011.
It's envisioned that the Golden Dome system will have both ground and space-based capabilities that can identify and stop missiles at four major stages of a potential attack:
- Detecting and destroying them before they are launched
- Intercepting weapons in early and mid-stages of flight
- Stopping them mid-course in the air
- Halting them in the final minutes before they fall toward a target
The US president said the system would be able to intercept missiles "launched from the other side of the world, or launched from space".
The head of the US Space Force, General Chance Saltzman, told politicians in Washington on Tuesday that the space-based weapons planned for the system "represent new and emerging requirements for missions that have never before been accomplished by military space organisations".
Mr Trump's announcement on Tuesday, alongside US Secretary of Defence Pete Hegseth, marks the start of the testing and purchasing phase for the system.
The US Congressional Budget Office estimated that just the space-based components could cost as much as $US542 billion over the next 20 years.
An initial $US25 billion for the program has been requested by Mr Trump in his proposed tax break bill now moving through Congress.
The specifics of the final system are yet to be released publicly, with US Air Force Secretary Troy Meink telling senators on Tuesday that the project is "still in the conceptual stage".
Experts have told the BBC and New York Times the scale of the Golden Dome will create significant technological challenges to implement in comparison to the Iron Dome, which covers a much smaller area.
Canada was also interested in the Golden Dome plan.
A statement from the office of Prime Minister Mark Carney said it had been raised during discussions about a new security and economic relationship.
"These discussions naturally include strengthening NORAD and related initiatives such as the Golden Dome," it said.
China raises legal concerns over plans
China's foreign ministry added on Wednesday, local time, that Golden Dome violated the Outer Space Treaty (OST), which outlines a framework for law in space.
The OST prohibits countries from putting nuclear weapons or weapons of mass destruction into orbit on celestial bodies or stationing them in space.
Christopher Newman, a professor of space law and a policy expert at Northumbria University, told the ABC any plan with space-based weapons would attract attention.
"It's not only China that will be concerned about this — Europe will be concerned about this," Professor Newman said.
He said whether or not Golden Dome violated the OST would come down to its final design and the extent of its space-based weapons.
"We need a lot more flesh on the bones on what Golden Dome is going to look like and what the technical requirements are, and then we can start thinking about the legality," he said.
"I think it's going to be technology and engineering (challenges) that's going to prevent it (going ahead), rather than law and diplomacy," he said.
ABC/wires
